A micro-electro-mechanical system (MEMS) accelerometer is an accelerometer fabricated using MEMS technology. With advantages such as small size, light weight, and low power consumption, the MEMS accelerometer is widely applied to vibration detection, azimuth detection, consumer application, motion recognition, and other fields.
A piezoresistive accelerometer is fabricated using the piezoelectric effect of lead zirconate titanate (PZT). When the PZT is under pressure, a resistance value of the PZT changes. By a bridge connection of piezoresistors, a change in resistance value is converted to be a change in voltage. After detection, amplification, and correction, a binary digital signal corresponding to an acceleration value is outputted. An induced voltage signal outputted by the accelerometer is generally around a few millivolts or tens of millivolts, which is very weak. And if it is directly inputted into an analog-to-digital circuit (ADC), then a dynamic range of an output will be low, and an accuracy of the output declines. Therefore, the induced voltage signal must be amplified before being inputted into the ADC, and finally an accurate digital signal corresponding to the induced voltage is obtained.
An analog front-end (readout circuit) of a conventional accelerometer generally consists of an amplification circuit and an ADC. Noise of a harmonic frequency of a control clock signal is introduced into the system, meanwhile, there is much noise of low frequencies in the environment (for example, a sound signal), if not filtered, a detected acceleration signal will be affected. If a filter circuit is introduced, resistors and capacitors applied to a filter capacitor will lead to an oversized a chip. A sensor is in a working state all through a signal processing process, which results in a great power consumption.
The front-end amplification circuit does not remove low-frequency 1/f noise or an input offset voltage, or use a buffer circuit having a large capacitor and based on Auto-Zero technology and correlated double sampling (CDS), which results in a large area of the circuit, and makes the circuit not easy to be integrated.
1/f noise and the input offset voltage of the amplification circuit itself are amplified a same ratio as the signal, therefore a signal-to-noise ratio decreased, and dynamic performance declined. The amplification circuit has a fixed gain, such that for different ranges of sensors, resolution for small signals is not enough.